This invention relates to a method of ethynylation of aromatic rings. More particularly, this invention relates to a method of ethynylating aromatic rings by reacting a protected acetylenic carbinol with a halogen substituted aromatic aldehyde to yield a protected ethynyl aromatic aldehyde, which can be subsequently deprotected to yield an ethynyl aromatic aldehyde.
The synthesis of ethynyl aromatic aldehydes is of importance because these compounds may be used to make Schiff's base resins which polymerize into highly useful materials, e.g., conducting polymers. The current method of ethynylating aromatic compounds is described by Austin et. al., J. Org. Chem. 46, 2280 (1981), who react a starting material, such as 3-bromobenzaldehyde, with a two-fold excess of ethynyltrimethylsilane in the presence of palladium(II) acetate and triphenylphosphine. This step is carried out in deaerated, anhydrous triethylamine at reflux under argon. The 3-[(trimethylsilyl) ethynyl] benzaldehyde thus formed is treated with base in anhydrous methanol to give the corresponding ethynylated benzaldehyde. This method suffers the dual disadvantages of expensive reagents and environmentally damaging waste products. There is currently a great need for a method of ethynylating aromatic compounds using inexpensive reagents and producing limited environmentally harmful waste.
Accordingly, it is an objective of the present invention to provide a method of ethynylating aromatic aldehydes without using expensive reagents or producing unnecessary environmentally damaging waste.